1. Field of the Invention
The invention relates to umbrella frame and more particularly to a telescopic shank of a collapsible umbrella, the shank being made of fiberglass-reinforced plastic (FRP) having advantages including insulation, being rust proof, weight, smooth opening and closing operations, and prolonged useful life.
2. Description of Related Art
Umbrellas are personal articles. An umbrella can be collapsible or non-folding. An umbrella typically includes a shank, a rib assembly, and a canopy secured onto the rib assembly. A collapsible umbrella includes a folding rib assembly and a telescopic shank. A non-folding umbrella has a shank of fixed length. Shank of an umbrella can be made of metal or fiberglass-reinforced plastic (FRP). Shank of a collapsible umbrella comprises an outer tube, an inner tube, and a moving mechanism mounted in the inner tube. Typically, the inner tubes of small umbrellas are made of metal. Large umbrellas (e.g., golf umbrellas) have a shank of greater diameter, and a large rib and stretcher assembly. Thus, they are heavy. It is labor consuming for a user carrying a large umbrella for a long distance walk. Therefore, both the inner tube and the outer tube of a shank of a large umbrella (e.g., golf umbrella) are made of FRP.
U.S. Pat. No. 6,866,053 entitled “Beach Umbrella Having Telescopic Shank” discloses a telescopic shank made of FRP wherein both the inner tube and the outer tube have eccentric section so that they can be fastened together. However, its manufacturing is difficult because eccentric tubes cannot be easily molded due to different wall thicknesses. Further, fibers are not uniform in length. Furthermore, polymers of FRP are not uniformly mixed in the manufacturing process. Thus, precision of both the inner tube and the outer tube is poor and tolerances are large. As a result, both the inner tube and the outer tube tend to malfunction after a time of use.
Further, metal shank can be machined but FRP shank cannot be machined. Thus, positioning of the inner tube and the outer tube and positioning of the inner tube and the moving mechanism are impossible for FRP shank. Therefore, no disclosure of telescopic FRP shank of an umbrella is available. To the contrary, improvements with respect to weigh reduction of a large umbrella are made continuously. As a result, length reduction of an umbrella shank made of FRP is not possible as the present inventor is aware.
For reducing weight of umbrella shank, using aluminum alloy or other light metal materials as raw material for manufacturing umbrellas is possible. However, its manufacturing cost is several times of that of FRP frame. That is, its market survivability is low due to competitiveness. Thus, how to devise a light umbrella having a telescopic shank without the drawbacks of large umbrellas is always desirable among manufacturers in the art.
Typically, a type of large umbrella has all components made of FRP except the spring. However, actions between the inner tube and the moving mechanism are not smooth. To the contrast, most components of small umbrellas are made by machining thin metal blanks. Small umbrellas thus have drawbacks of being weak, being susceptible to being damaged by strong winds, susceptible to being rusted, and being susceptible to being injured by thunder.
The invention discussed below aims at providing a collapsible umbrella with a telescopic shank made of FRP having advantages including insulation, being rust proof, and light weight, thereby eliminating all drawbacks associated with conventional large umbrellas.